The present invention relates to a method and apparatus for electronic temperature sensing and recording. More specifically, the present invention is directed to reducing the dynamic range required for an analog-to-digital converter that is used to measure the effects of temperature changes upon a forward-biased PN junction of a temperature sensor where two current levels are used to bias the PN junction.
Temperature sensors are often employed to measure temperatures in a remote system. One type of temperature sensor includes a semiconductor device such as a PN junction. A PN junction conducts a current when forward biased. The PN junction has an associated voltage drop that is determined by the forward bias current and the temperature of the PN junction. Voltage drops across the PN junction are measured for two different forward bias currents. An analog-to-digital converter (ADC) may be employed to convert the voltage drops across the PN junction to digital data. The digital data is recorded and analyzed to determine the temperature of the PN junction.
The present invention is directed to a method and apparatus for electronic temperature sensing. More specifically the present invention is directed towards a method and apparatus that reduces the dynamic range required by an analog-to-digital converter (ADC).
In one example, a converter system for a temperature sensor includes a programmable current source, a digital-to-analog converter, a summer, and an analog-to-digital converter. The temperature sensor provides a measurement voltage in response to application of a bias current. The programmable current source selectively provides two different currents to the temperature sensor such that the temperature sensor provides two measurement voltages during a given temperature measurement. The digital-to-analog converter (DAC) provides an intermediate voltage that corresponds to an approximation of a voltage between the two voltages. A summer is configured to produce an offset measurement in response to the intermediate voltage and the measurement voltage. The analog-to-digital converter (ADC) receives the offset measurement voltage and produces a conversion code. Offsetting the measurement voltage reduces the dynamic range requirements of the ADC such that substantially a full input range of the ADC is utilized.